Epidermal gene regulation mediates homeostasis between progenitor proliferation and differentiation. AR45192 efforts identified 2 new epidermal gene regulators, ZNF750 and PRMT1. ZNF750 is mutated in human diseases characterized by abnormal epidermal differentiation. We found ZNF750 to be the most highly induced putative transcription factor in epidermal differentiation and to act in a complex with KLF4 and other proteins to control this process. The PRMT1 arginine methyltransferase was found to simultaneously sustain expression of progenitor genes while repressing differentiation. In epidermal progenitors, PRMT1 resided within its own complex, which includes CSNK1A1, a kinase, that also recapitulated PRMT1 impacts. This competing renewal will characterize how these gene regulators and their interactors effect homeostatic epidermal gene regulation. First, we will define mechanisms whereby ZNF750 regulates epidermal differentiation. Mass spectrometry of independently purified ZNF750 and KLF4-binding proteins discovered a direct ZNF750-KLF4 interaction and identified additional interactors. ZNF750 is only expressed in stratified epithelia, suggesting that ZNF750 binding to KLF4 could account for the contrast between KLF4's function in pluripotent cells and its essential role in epidermal differentiation, a possibility which would provide insight into how transcription factors are re-purposed in different biologic contexts. Aim I will test the hypotheses that specific ZNF750-KLF4-binding proteins help control epidermal differentiation and that ZNF750 converts KLF4 from a pluripotency factor to a driver of epidermal differentiation by re-targeting its genomic binding. Second, we will determine how PRMT1 sustains epidermal progenitor gene expression. Recent AR45192 efforts discovered an essential role for arginine methylation in epidermal progenitor function via PRMT1. Purification of the PRMT1 protein complex identified CSNK1A1 and 36 other PRMT1-binding proteins. The full function of the PRMT1 progenitor maintenance complex (PPMC) requires the catalytic activity of both the PRMT1 methyltransferase and the CSNK1A1 kinase, however, the spectrum of their target substrates in epidermal gene regulation is unknown. Aim II will test the hypotheses that additional proteins within the PRMT1 complex help sustain the epidermal progenitor state and that PRMT1 and CSNK1A1 modify specific targets to effect progenitor maintenance. This proposal will define how these new dominant regulators of epidermal gene regulation sustain epidermal homeostasis, as a basis for future therapies for diseases of the skin.